This invention is in the field of cargo-carrying trailers and particularly trailers that are vertically adjustable.
Most trucks and trailers today are individually owned and are operated on a lease and percentage basis, particularly in oil field equipment handling. The majority of truckers around the oil fields own only one truck and one type of trailer although there are various types and sizes of loads to be handled in oil fields. A flat-bed type trailer cannot haul an overly high load such as a sub-structure for drilling rigs whereas a trailer suitable for hauling such structures cannot easily haul lengths of pipe or casing since the hauling of such on a short but low-bedded trailer is considered dangerous. Most truckers cannot afford to own different types of trailer.
It has been proposed heretofore to construct trailers, the beds of which can be elevated or lowered but principally for the purpose of convenience in loading heavy cargo on the trailer, then lifting it to a suitable height for transportation. See, for example, the following U.S. patents:
U.S. Pat. No. 2,475,443--Bill PA1 U.S. Pat. No. 3,429,585--Ross PA1 U.S. Pat. No. 3,517,944--Hage PA1 U.S. Pat. No. 4,003,583--Stanzel PA1 U.S. Pat. No. 4,050,707--Glumac PA1 U.S. Pat. No. 4,061,353--Kingman et al
The above patents, however, do not disclose trailers that can be converted from a low-bed trailer suitable for hauling bulky loads to a flat-bed trailer suitable for hauling long lengths of pipe or casing or the like.